In storing an airplane in a hangar, or while handling the airplane on the ground, the long wingspan is a disadvantage, limiting the flexibility of use and a more universal utilization of the airplane on the ground. The need for a design which will allow a substantial reduction of the wing span on the ground is obvious. Various design alternatives for reduction of the wing span, such as folding wings, which are used on military aircraft on carriers have been developed, and while the geometry and mechanism for folding wings is relatively simple, the concept is not suitble for applications where the aircraft is moved about on the ground at highway speeds. For one thing, wings folded up against the side of the fuselage present a large surface area which can be affected by side winds; and the center of gravity is raised or moved rearwardly, which is detrimental.
Another concept for reducing the wing span is to telescope the wing, which has the possibility of substantially contracting the span without many of the structural and other disadvantages of the folding wing. The center of gravity of the telescopic wing is not changed, and the side area affected by winds does not exist.
Various attempts have been made in the past to design a telescoping wing, but these have not been successful. One such attempt divides each wing into two sections, with the outer section being divided into several smaller spanwise sections which are telescoped into the inner section. In this design, the spars necessarily have a fairly large overlap due to their sliding relationship, and this reduces the total amount of span reduction so that the retracted wing is still more than 50% of the extended wing span. This is not enough of a span reduction to amount to a substantial improvement.
Another prior attempt at providing a telescopic wing used a plurality of wing sections, each consisting of the skin, a rib, and a tubular portion with an internally threaded collar at its end that meshes with threads on a short tubular spar section. The tubular spar sections are connected to one another, and are rotatable with respect to one another. Extension and retraction of the spar sections is supposed to be accomplished by rotating the innermost spar section, which is then supposed to screw into the next adjoining spar section. However, without some means to hold one spar section against turning while the next adjoining spar section is rotated, there can be no screwing together or apart. Because the spar is made up of several short tubular sections, each of which is rotatably connected to the next adjoining spars at both ends, the spar assembly has no torsional rigidity, and apparently torsional loads are supposed to be carried by the skin, which is completely impractical, since the skin sections are connected by rollers.
Several other concepts have been proposed, but each of them has had structural or other problems that have made the designs impractical, and therefore they have never been reduced to practice. Thus, while the telescoping wing appears to have many advantageous features, there has never been a practical design that could realize its advantages.